The overall objective of the research is to elucidate determination process in early embryogenesis at the molecular level. Programming of DNA templates in chromatin for RNA synthesis is postulated to play a role in the process. Sea urchin embryos are used as a model system for the study. Changes in chromatin properties which may occur right after fertilization as the initial step in embryonic determination will be examined by in vivo labelling of chromosomal proteins, biochemical isolation and characterization, and autoradiography. As an exploratory study, determination processes involved in acetylcholinesterase differentation in sea urchin embryos will be examined. How does the enzyme activity increase? When does its differentiation become determined? What changes in chromatin may correspond to this determination? The study is intended to expand our understanding of the basic mechanism underlying early embryogenesis and useful application may be found in the prevention of defects in human development.